The disclosure relates to vapor compression systems. More particularly, the disclosure relates to purge units for removing contaminants from vapor compression systems.
Many vapor compression systems using low vapor pressure refrigerants include purge units for removing noncondensable contaminants from the system. A flow is diverted from the main refrigerant flowpath and passed into a purge tank where it is cooled to condense refrigerant while leaving noncondensable contaminants in vapor form. The vapor may be vented or pumped out of the vessel (e.g., to atmosphere). The purge unit may operate intermittently.
The condensing heat may be removed by a secondary vapor compression system. The secondary vapor compression system may have its own recirculating refrigerant flowpath proceeding downstream from a compressor to a heat rejection heat exchanger, an expansion device, a heat absorption heat exchanger providing the cooling for the purge tank, and then returning to the compressor.
One particular vapor compression system is used as a chiller to produce chilled water. An exemplary chiller uses a hermetic centrifugal compressor. The exemplary unit comprises a standalone combination of the compressor, a heat rejection heat exchanger, an expansion device, an evaporator unit, and various additional components. Exemplary compressors are electric motor-driven hermetic or semi-hermetic compressors.
WO2014092850A1 discloses chiller systems using low pressure refrigerant. WO2014092850A1 defines “low pressure refrigerant” refrigerant as having a liquid phase saturation pressure below about 45 psi (310.3 kPa) at 104° F. (40° C.) and gives an example of low pressure refrigerant as R245fa. It also references use of “medium pressure refrigerant” which it defines as having a liquid phase saturation pressure between 45 psia (310.3 kPa) and 170 psia (1172 kPa) at 104° F. (40° C.). A further recent low pressure refrigerant is HFO R1233zd(e).
Also, international patent application PCT/US14/43834, filed Jun. 24, 2014, discloses use of phase change material in association with an evaporator of a refrigeration system. Exemplary phase change materials include paraffin waxes, fatty acids from natural oils, and inorganic salt solutions. The exemplary phase change material has a melting temperature (from solid to liquid) at which it absorbs heat while maintaining a substantially constant temperature. In other words, as the phase change material is heated up from a temperature below the melting temperature to the melting temperature, the temperature of the phase change material rises accordingly. However, when the phase change material reaches its melting temperature, the temperature of the phase change material remains substantially the same as it absorbs heat, before all the phase change material becomes liquid.